Bending the new breedsof high-strength steelNew challenges, new tools, new rulesBy David Bishop

Since the early 1980s, sheet
metal fabricators have, for the
most part, followed a pretty
basic set of rules to air-bend
mild steel. To determine the appropriate die opening to bend 0.5-inch-
thick ( 12.7-mm) and thinner materials, you simply multiplied the material thickness times 8. To calculate the
resulting inside radius, you either
multiplied the width of the die opening times 16 percent, or divided it by
6. And one punch with a 0.031-in.
(0.8-mm) tip radius could bend nearly anything from 20- to 12-gauge mild
steel.

Bending steel plate pretty much
meant following those same set of
rules, except that you had to use
punches with larger tip radii, and
when the material thickness exceeded
0.5 in., you would multiply the material thickness times 10 to determine
the correct minimal die opening.

Several new breeds of high-strength steel have arrived that bring
with them a host of new opportunities. However, these new breeds also
bring with them special challenges
not common to bending mild steel,
and with them, the need for new tools
and new rules for proper bending,
because the traditional rules for determining minimum bend radius, minimum punch radius, die opening, bending force, and tooling requirements do
not always apply.

Construction-grade HSS is engineered to reduce the weight and
increase the lifting capacity in applications such as mobile cranes, truck
cranes, and trailers. Other HSSs are
engineered to increase the useful life
of equipment such as excavator buckets and truck beds.

Heavy-construction equipment
may be made of HSSs, such as
RAEX®, that are designed to provide
improved resistance to the abrasive
wear caused by soil, rock, crushed
aggregate, gravel, coal, and sinter.
Feeders and funnels, mining equipment, pruning blades, wood processing equipment, shredder blades, and
mixing blades may be constructed of
this new type of HSS.

Formability Requirements
and Special Considerations

So what are the high-strength steels’
unique forming requirements? If you
are considering taking on a job that
will require you to bend some of these
materials, it is advisable to consult
with the manufacturer or the technical staff at the steel service center
before ordering the first piece of material and to ask the following questions:

• What is the tensile strength?

• What is the yield strength?

•What is the minimum bend
radius?

•What is the recommended
punch radius?

•What die opening is recommended for the material thickness I
am planning to use?

• What effect does grain direction
have on forming this material?

So what purposes do these new breeds • What special considerations do I
of high-strength steel (HSS) serve? need to take into account?

Today’s new, stronger steels can reduce While all of these questions are
part weight, increase part strength, very important, you should pay very
extend part life, improve fatigue and close attention to the last one, because
crash performance, and resist abrasion. many special considerations for bend-

Some HSSs, such as Domex®, are ing these materials are not common to
designed to reduce the weight of bending mild steel. If these considera-heavy vehicles, trailers, cranes, and tions are ignored, problems could
containers. result:

The New Breeds of
High-strength Steel

BThis heavy-duty gooseneck punch
with an acute-angle 1V die provides the
ability to overbend material to compensate for springback.

The FABRICATOR | An FMA Publication
www.thefabricator.com | March 2007